1. Field of the Invention
The present invention relates to a developing unit of an electrophotographic processor, such as a laser printer, copier or plain paper facsimile. More particularly, the present invention relates to an apparatus which eliminates the electric charge of toner remaining on the surface of a developing roller.
2. Description of Background Art
Generally, a printer using an electrophotographic developing system includes a photosensitive drum on which a latent image is formed conductively when exposed to light. A charge roller supplies a high voltage to the photosensitive drum. An exposing unit irradiates a prescribed portion of the photosensitive drum to light energy corresponding to a character signal or an image signal transmitted from a computer. A developing roller adheres charged toner on the photosensitive drum. A transfer unit transfers the toner from the photosensitive drum onto a recording sheet with a high voltage differential. A fixing unit fixes the toner on the recording sheet with high voltage and pressure.
Exemplars of contemporary practice in the art include U.S. Pat. No. 5,604,573 for Developing Unit with a Smoothing Plate, issued to Endo et al., which a developing sleeve on which is superimposed a bias voltage. The device also includes a linear electrode member also having a bias voltage imposed thereon, with an assertion that it is preferable from a view point of toner adhering prevention that a DC voltage having the same polarity as that of the toner be impressed upon the linear electrode member 84." The DC voltage impressed upon the sleeve may be equal to the DC voltage impressed upon the linear electrode member.
U.S. Pat. No. 5,177,537 for Developing Apparatus with Elastic Regulating Member Urged to a Developer Carrying Member, issued to Okano et al., includes an elastic blade in contact with the developing sleeve. The elastic blade is coated with resin particles electrically chargeable to a positive polaity. The elastic blade is charged via friction with the toner particles on the developing roller. U.S. Pat. No. 4,806,992 for Developing Apparatus, issued to Yasuda et al., includes a developer supply roller with a grounded shaft. The supply roller has an electrostatically-induced negative charge which attracts positively-charged toner.
U.S. Pat. No. 4,930,438 for Developing Device Using a Single Component Developer, issued to Demizu et al., includes a discharging brush downstream of the developing station. The discharging brush is electrically connected to the bias voltage source so that a potential is maintained at the same level as that of the electrically-conductive support of the developing sleeve. U.S. Pat. No. 5,076,201 for Developing Device Used in Electrophotographic Field And Method of Producing Developing Roller Incorporated Therein, issued to Nishio et al., includes a blade member that contacts the developing roller. The blade member has a bias voltage applied across it so that charged toner particles are prevented from being electrostatically adhered to the blade member 20.
I have found that the toner remaining on the surface of the developing roller, after the electrostatic latent image formed on the surface of the photosensitive drum is developed, exhibits a strong negative charge and presents a ghost image which contaminates the next-forming image.